Wind turbines are usually equipped with lightning protection systems to ensure that the large currents induced by a strike of lightning can be conducted to ground without damaging the components of the wind turbine.
The parts exposed the most to lightning are the blades. Therefore, blades are equipped with one or more internal down conductors. Each down conductor is connected to one or more lightning strike receptors which are arranged at the outer surface of the blade.
To ensure proper function of the down conductor it is necessary to know its electrical resistance. According to international standards registration of the electrical resistance of each installed down conductor is mandatory.
The electrical resistance of a down conductor of a blade is usually measured from an outside tip receptor to the bottom part of the blade. The measurement is done with an ohm meter or with a known current and a detection unit. Sometimes the measurement results are shown with a red or green light or an alarm sound or bell. To access the tip receptor can be difficult especially for already installed blades.